JPH0212907B2 - - Google Patents

Description

[Detailed description of the invention]

(Prior art) Conventionally, glass fiber or asbestos products have been widely used as inorganic insulation foam materials, but since these products easily absorb water, they absorb moisture and have high thermal conductivity in humid environments. The drawback was that the heat insulation effect suddenly decreased. In addition, non-water-absorbing products include foam glass (manufactured by Pittsburgh Corning, USA), which is made of foamed glass obtained by foaming glass.
This product does not absorb moisture even in humid environments, and therefore has low thermal conductivity. However, since such conventional foam glass uses waste glass or glass cullet with a low aluminum oxide content (less than 5%), it easily breaks due to temperature shock, causing cracks, and is difficult to create into complicated shapes during manufacturing. Because of the disadvantages of being difficult to mold, requiring a long time to cool, and being expensive, it could only be used for special purposes such as cryogenic insulation. For example, as described in Japanese Patent Publication No. 55-40550, by adding blast furnace slag to a shirasu-water glass composition and firing it to foam, and precipitating microcrystals, bubble stabilization and product quality are achieved. Although it has been proposed to obtain crystallized foam glass with increased strength, a heat insulating material with a low specific gravity (0.4 or less) cannot be obtained, and the above-mentioned drawbacks of foam glass cannot be fundamentally solved. (Problems to be solved by the present invention) The present invention has a low specific gravity (0.4 or less), a high closed cell ratio (50% or less), and a uniform cell diameter, with the cell diameters inside and near the surface being almost the same. The purpose of this invention is to provide a method for producing an inorganic heat-insulating foam material that is lightweight, has excellent heat insulation properties, and can be easily formed into complex shapes during production. (Means for Solving the Problems) The gist of the present invention is to add 0.3 to 5 parts by weight of silicon carbide or/and silicon nitride to 100 parts by weight of natural glassy mineral, and vanadium pentoxide or/and leadous oxide.
A composition containing 0.1 to 5 parts by weight and 50 parts by weight or less of water is pressure molded at a pressure of 0.1 to 2000 Kg/cm ² , and then the molded product is heated to the firing temperature of natural glassy minerals. The present invention relates to a method for producing an inorganic heat-insulating foam material, which comprises melting and foaming the material, followed by cooling. Examples of the natural glassy minerals used in the present invention include shirasu, obsidian, and flint, and the average particle size is 100 μm or less, preferably 46 μm.
m or less is preferably used. Average particle size
If a material with a diameter exceeding 100 μm is used, it is difficult to obtain a foam material with a high closed cell ratio, and the foam material tends to have many open cells. As the silicon carbide and silicon nitride used in the present invention, those having a particle size smaller than the average particle size of natural glassy minerals, a purity of 75% or more, and a residual carbon of 5% by weight or less are preferably used. If a material with a particle size larger than the average particle size of natural glassy minerals is used, it is difficult to obtain a foam material with a high closed cell ratio, and the foam material tends to have many open cells. Note that silicon carbide and silicon nitride can be used alone or in combination. In addition, silicon carbide and silicon nitride are natural glassy minerals.
It is necessary to add 0.3 to 5 parts by weight per 100 parts by weight. If the amount added is less than 0.3 parts by weight, only a product with a high specific gravity can be obtained, and if it exceeds 5 parts by weight, a foamed material with a high closed cell ratio cannot be obtained, and a foam with many open cells will be obtained. I end up. As vanadium pentoxide and first lead oxide used in the present invention, those having an average particle size smaller than the average particle size of natural glassy minerals are preferably used. If a natural glassy mineral with a particle size larger than the average particle size is used, it is difficult to obtain a foamed material having uniform cells. Incidentally, vanadium pentoxide and first lead oxide can be used alone or in combination. Further, it is necessary to add vanadium pentoxide and first lead oxide in an amount of 0.1 to 5 parts by weight per 100 parts by weight of natural glassy mineral. If the amount added is less than 0.1, uniform cells will not be obtained, and if it exceeds 5 parts by weight, a foamed material with a high closed cell ratio will not be obtained and will have many open cells. In the present invention, a binder and water are added as necessary. The binder and water are used to maintain the effect of pressure molding, which will be described later. As a binder, water-soluble polymers such as polyvinyl alcohol, polyethylene oxide, or cellulose derivatives (methylcellulose, carboxymethylcellulose, hydroxycellulose,
or crystalline cellulose). The amount of binder added is 10 parts by weight or less per 100 parts by weight of natural glassy mineral. The amount of water added is 50 parts by weight or less per 100 parts by weight of natural glassy mineral. The amount of binder and water added is determined by the pressure of pressure molding, and in order to maintain the effect of pressure molding, if the pressure is low, it is necessary to increase the amount added, and as the pressure approaches 500Kg/cm ² , the amount of water added will gradually increase. A small amount is sufficient, and it is not necessarily necessary if the amount is 500Kg/cm ² or more. In the present invention, the above composition is added to 0.1% before firing.
It is necessary to perform pressure molding at a pressure of 2000 kg/cm ² to 2000 kg/cm 2 . This pressure molding process is an essential process to obtain a foamed material with a high closed cell ratio, and it also prevents cracks in the structure of the molded product due to the internal gas pressure until the temperature is raised to the firing temperature. prevent this from occurring. This molded product is heated and foamed in a firing furnace such as an electric furnace to 1000 to 1200°C, which is the firing temperature of natural glassy minerals, and then taken out from the firing furnace and slowly or rapidly cooled to produce the desired inorganic insulation. Get foam. In the present invention, (1) the main raw material is a natural glassy mineral; (2) the amount of silicon carbide and silicon nitride added is 0.3 to 5 parts by weight per 100 parts by weight of the natural glassy mineral; (3) The amount of vanadium pentoxide and lead oxide added is 0.1 to 5 parts by weight per 100 parts by weight of natural glassy mineral, (4) The composition containing these should be added in an amount of 0.1 to 20 kg/cm ^{2 .} Pre-pressing under pressure is a very important requirement. By adopting the method of the present invention that satisfies these requirements, for the first time, the specific gravity is as low as 0.4 or less.
Moreover, it is possible to produce a lightweight inorganic heat-insulating foam material with a high closed cell ratio of 50% or more, a uniform cell diameter, and a cell diameter of approximately the same inside and near the surface, which is lightweight and has excellent heat insulation properties. This fact is considered to be based on the following principle. That is, when a natural glassy mineral, silicon carbide or/and silicon nitride, and vanadium pentoxide or/and lead oxide are mixed, a large number of silicon carbide and/or silicon nitride particles are formed around the natural glassy mineral particles. A mixed composition is obtained in which particles and a large number of particles of vanadium pentoxide or/and lead oxide are attached.
When this composition is press-molded in advance at a pressure of 0.1 to 2000 kg/cm ² in this state, silicon carbide or/and silicon nitride, and vanadium pentoxide or/and leadous oxide are formed between the particles of the natural glassy mineral. The particles are packed together and form a close contact state. In such a state, when the temperature is raised to the firing temperature of natural glassy minerals, vanadium pentoxide and/or lead oxide lowers the surface tension of the natural glassy minerals in the molten state, and the foamed silicon carbide or / and silicon nitride are uniformly dispersed to melt and connect the inorganic components of the natural glassy mineral. Next, the foaming agent foams appropriately in the foam, resulting in foaming with a high closed cell ratio, which has a low specific gravity, little connection between the cells, and uniform cells, with the cell diameters on the inner surface and near the surface being almost the same. The material is formed. (Example) Hereinafter, the present invention will be explained with reference to Examples. Examples 1 to 3 As a natural glassy mineral, the particle size is 46 μm or less.
Silicon carbide (BFC: Pacific Random Co., Ltd.), silicon nitride (TS-7: Toyo Soda Co., Ltd.), vanadium pentoxide (reagent grade 1:
(manufactured by Hanui Chemical Co., Ltd.), lead oxide (reagent 1st grade manufactured by Wako Pure Chemical Industries, Ltd.), and water, respectively.
A composition was obtained by mixing the amounts shown in the table. Each of these compositions was heated to a pressure of 10% using a hydraulic press.
After pressurizing for 3 minutes at Kg/cm ² , the mold was removed, and the dimensions were 148 mm in diameter.
It was made into a disk-shaped molded product with a thickness of 10 mm. Each of these molded products was placed in an electric furnace and heated to 1120°C at a heating rate of 150°C/hr, held at that temperature for 30 minutes to fire and foam, and then cooled and taken out to form inorganic insulation foam. I got the material. These inorganic heat-insulating foam materials were evaluated by measuring their appearance (uniformity of cells), specific gravity, closed cell ratio, and thermal conductivity in steady state and after water absorption. The closed cell ratio was 0.4 or less, the closed cell ratio was 50% or more, and the water absorption rate was low, so the thermal conductivity hardly changed after water absorption. The evaluation method for the inorganic heat insulating foam material is as follows. (All test pieces were prepared with the epidermis removed.) (1) Specific gravity A test piece measuring 40 mm x 40 mm in length and width and 20 mm in thickness was heated at 105℃.
The weight (Wg) and volume (V
cm ³ ) was measured, and the specific gravity was determined using the following formula. Specific gravity (g/cm ³ ) = W/V (2) Closed cell ratio A test piece of 40 mm x 10 mm in length and width and 15 mm in thickness was
First, measure the volume (Vcm ³ ) in a constant temperature room at ℃ and RH 60%, then measure the volume (Vbcm ³ ) using an air comparison hydrometer (manufactured by Toshiba Beckman), and calculate the closed cell ratio using the following formula. Ta. Closed cell ratio (%) = Vb/V (3) Thermal conductivity A test piece of 45 mm x 100 mm in length and width and 20 mm in thickness was
Measurement (λm) was performed using a QTM rapid thermal conductivity meter (manufactured by Showa Denko) in a constant temperature room at ℃ and RH 60%, and the thermal conductivity in a steady state was determined using the following formula. Thermal conductivity (kcal/mh℃) = λm x A-B A and B are correction values In addition, after soaking the test piece in water for 24 hours to absorb water,
The thermal conductivity after water absorption was measured according to the above procedure. (Comparative Example) An inorganic heat-insulating foam material was obtained and evaluated in the same manner as in Example 1, except that vanadium pentoxide and first lead oxide were not added. The results are also shown in Table 1. In the case of the comparative example, the inside of the inorganic heat-insulating foam material was foamed uniformly, but there was almost no foaming near the surface layer, forming a skin layer, resulting in a non-uniform foaming state as a whole compared to Example 1.

[Table] (Effects of the invention) Since the method for manufacturing the inorganic heat insulating foam material of the present invention has the above-described configuration, the specific gravity is as low as 0.4 or less, the closed cell ratio is high as 50% or more, and the cell diameter is uniform. The cell diameters inside and near the surface are almost the same, making it possible to produce an inorganic heat-insulating foam material that is lightweight, has excellent heat insulation properties, and is easy to mold into complex shapes during production. We can manufacture heat insulation covers, etc.

Claims (1)

[Claims] 1. 0.3 to 5 parts by weight of silicon carbide or/and silicon nitride, 0.1 to 5 parts by weight of vanadium pentoxide or/and first lead oxide, and 50 parts by weight or less of water were added to 100 parts by weight of natural glassy mineral. composition, 0.1
A method for producing an inorganic heat-insulating foam material, which comprises press-molding at a pressure of 2000 Kg/cm ² to 2000 Kg/cm 2 , then heating the molded product to the firing temperature of natural glassy minerals, melting and foaming it, and then cooling it. .